Research On CO₂Capture By Task-specific Ionic Liquids And Modifid Mesoporous Silicon Materials

Since CO2is one of the most important greenhouse gases, the research and development in thecarbon capture technology have long been the focus of many academic and industrial studies. Solventabsorption and solid sorbent adsorption technology have been implemented and modified for the carboncapture. Ionic liquids have a number of unique properties, such as no-volatility, non-flammation,recyclability, high thermal stability, strong solubility capacity, and the tunability of molecularstructures andphysicochemical properties, and therefore have broad prospect in the absorption and separation of CO2. Inaddition, silicon modified mesoporous materials have also been widely concerned in the field of CO2capture due to its high absorption performance and high selectivity. The morphology of silicon-basedmesoporous materials were redesigned to adjust pore structure, morphology and structure in order to studythe impact on the adsorption properties and optimize CO2diffusion in the pore. In this work, functionalionic liquids were applied to capture CO2by physical or chemical action. In addition, by expanding thepore size and shorten the mosochannels, we developed the new mesoporous materials with high CO2capture capacity, high selectivity, high adsorption-desorption dynamics. Details are as follows:1. Ionic liquids1-n-butyl-3-methylimidazolium heptafluorobutyrate [C4mim][CF3CF2CF2COO]and1-n-butyl-3-methylimidazolium nonafluorobutyl sulfonate [C4mim][CF3CF2CF2CF2SO3] have beensynthesized and characterized by1H and13C NMR spectra. Solubilities of CO2, H2, N2and O2in these ILshave been determined at the temperature range from (293.15to343.15) K and the pressure up to8.9MPa.From these data, the Henry’s constant, the standard state solution Gibbs energy, standard state solutionenthalpy and standard state solution entropy of these gases in [C4mim][CF3CF2CF2COO] and[C4mim][CF3CF2CF2CF2SO3] were derived and analyzed from molecular interactions. And the solubilityselectivites for CO2relative to O2, N2and H2in both of ILs were calculated. The CO2solubility in these ILwas compared to other ILs sharing the same cation. This comparison shows that the solubility of CO2inthese ILs follows the sequence:[C4mim][CF3CF2CF2CF2SO3]=[C4mim][Tf2N]>[C4mim][CF3CF2CF2COO]>[C4mim][CF3COO]>[C4mim][CF3SO3]>[C4mim][BF4]. It is indicated thatthis kind of ILs would be a promising absorbents for CO2viewing from the absorption capacity andselectivity performance. Furthermore, these solubility data were well correlated by Pitzer model and Krichevsky-Kasarnovsky equation.2. The adsorption capacities of AAILs have been greatly enhanced by dispersed on themesoporous silica material SBA-15with special pore structures and large specific surface area. The CO2capture capacity reached up to0.91mol CO2per mol IL by forming carbamic acid in a ratio of one CO2perone amine (1:1stoichiometry) since SBA-15can disperse AAILs molecules from the bulk of the liquidphase to the surface of the support and separate them fully. In addition, CO2capture capacity can be finelytuned via AAIL loading and sorption temperature. Furthermore, the captured CO2can be released byheating under vacuum, and the adsorbent is quite stable after five adsorption-desorption cycles. The presentstudy provides a new approach for equimolar CO2capture of amine-functional ILs by the combination of asolid nanoporous material, which may provide an industrially attractive alternative for CO2capture of ILs.3. To enhance CO2adsorption capacity, a kind of platelet SBA-15with short channels and largepore diameter has been prepared and then grafted with various aminosilanes (mono-, di-, andtri-aminosilanes). Thorough analysis of the support structure and sorbent performance was estimatedthrough a combination of amine loading and CO2adsorption capacity and CO2/N2selectivity. It was shownthat compared to traditional SBA-15, the increase in amine loading CO2adsorption capacity can be up to66%and120%, respectively, for these novel sorbents, and the selectivity of CO2/N2was remarkablyenhanced from37to169. The CO2adsorption enthalpy reached67kJ mol1which suggests thatchemisorption was the predominant process. Moreover, these sorbents are regenerable and exhibit goodstabilities. Thus, this approach offers an alternative for the development of technological innovationtowards efficient and reversible processes for carbon capture.